Toothpaste manufacturers strive to produce dentifrices with high cleaning and low abrasivity. Such formulators achieve this goal by incorporating abrasive substances into the toothpaste formulation. An abrasive substance has been included in conventional dentifrice compositions in order to remove various deposits, including pellicle film, from the surface of teeth. Pellicle film is tightly adherent and often contains brown or yellow pigments, which impart an unsightly appearance to the teeth. While cleaning is important, the abrasive should not be so aggressive so as to damage the teeth. Ideally, an effective dentifrice abrasive material maximizes pellicle film removal while causing minimal abrasion and damage to the hard tooth surfaces. Consequently, among other things, the performance of the dentifrice is highly sensitive to the abrasive polishing agent ingredient.
A number of water insoluble, abrasive polishing agents have been used or described for dentifrice compositions. These abrasive polishing agents include natural and synthetic abrasive particulate materials. The generally known synthetic abrasive polishing agents include amorphous precipitated silicas, silica gels, dicalcium phosphate and its dihydrate forms, calcium pyrophosphate and precipitated calcium carbonate (PCC). Other abrasive polishing agents for dentifrices have included chalk, magnesium carbonate, zirconium silicate, potassium metaphosphate, magnesium orthophosphate, tricalcium phosphate, and the like.
Synthetically produced amorphous precipitated silicas, in particular, have been used as abrasive components in dentifrice formulations due to their cleaning ability, relative safety, and compatibility with typical dentifrice ingredients, such as humectants, thickening agents, flavoring agents, anti-caries agents, and so forth. Synthetic precipitated silicas generally are produced by the de-stabilization and precipitation of amorphous silica from soluble alkaline silicate by the addition of a mineral acid and/or acid gases under conditions in which primary particles initially formed tend to associate with each other to form a plurality of aggregates (i.e., discrete clusters of primary particles), but without agglomeration into a three-dimensional gel structure. The resulting precipitate is separated from the aqueous fraction of the reaction mixture by filtering, washing, and drying procedures, and then the dried product is mechanically comminuted in order to provide a suitable particle size.
Such previously produced and utilized precipitated silica abrasives have been produced and provided for dentifrices generally in terms of overall cleaning and abrasive qualities. Although such previous products have accorded excellent benefits in these areas, it has been noted that certain limitations in terms of production costs and waste generation are prevalent as a result. For instance, in order to target specific lower abrasive levels, milled particles include materials that exhibit particle sizes outside the required ranges. Proper filtering and disposal of such undesirable materials are thus needed. The same types of production issues and problems arise when targeting certain lower abrasive levels for particulate materials without sacrificing pellicle film cleaning as well. As it concerns the ability to provide less costly production methods for providing such effective low-abrasion, high pellicle film cleaning materials to users susceptible to unwanted dentin abrasion at the gum line, as well as potential supplemental abrasive/cleaning silica products for more effective polishing and/or tooth whitening applications, the industry has been reliant upon outdated methods of production, separation, and disposal of undesirable particles. As a result, there are areas within the dental silica materials industry in which improvements to such ends are desired.
Given the foregoing, there is a continuing need for a method of producing precipitated silica materials that provide excellent cleaning performance, but with lower abrasivity values, that can be included in a toothpaste composition. To that end, the following invention has proven to accord such coveted results.